Polymers and the use thereof as lubricating agents in the production of alkali metal films

ABSTRACT

Polymers used as rolling lubricating agents, to compositions including said polymers, and to alkali metal films including the polymers or compositions on the surface(s) thereof. The use of said polymers and compositions is also described for strip-rolling alkali metals or alloys thereof in order to obtain thin films. Methods for producing said thin films, which are suitable for use in electrochemical cells, are also described. An improved lubricant according to formula I, which, for example, achieves enhanced conductivity, and/or enables the production of electrochemical cells having an improved life span in cycles.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.16/158,996, filed on Oct. 12, 2018, which is a continuation of U.S.application Ser. No. 15/300,412, filed 29 Sep. 2016, now U.S. Pat. No.10,106,758, which is a U.S. national stage of International ApplicationNo. PCT/CA2015/050256, filed on 31 Mar. 2014, which claims priority tothe provisional U.S. Application No. 61/973,493, which is incorporatedhere by reference in its entirety and for all purposes. The entirecontents of each of U.S. application Ser. No. 16/158,996, U.S.application Ser. No. 15/300,412, U.S. Provisional Application No.61/973,493, and International Application No. PCT/CA2015/050256 arehereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The technology relates to the field of polymers and to their use aslubricating agents for rolling (between rollers) and to the compositionsincluding them. The technology also relates to films of alkali metals,including the lubricating agents and/or the composition on one surfaceor on the two surfaces thereof. The technology is also connected withthe methods for producing thin alkali metal films or alloys thereof,including the use of the lubricating agents and of the compositions, andwith the films thus produced, which are suitable for use inelectrochemical cells.

Context

The production of thin lithium films in the form of broad bands, and inlengths of several tens of meters by rapid and reliable processes facesserious technical difficulties attributable to the extreme physical andchemical properties of this metal: chemical reactivity, malleability,rapid self-welding by simple contact, and strong adhesion to most solidmaterials, including the usual metals.

The previous rolling methods as described in the U.S. Pat. No.3,721,113, use rollers made of hard plastic or of plastic-coated metal,but successive passes of the film between the rollers were needed inorder to obtain a film of about 30 to 40 μm. Processes based on thecoating of molten lithium on a metal or plastic support have also beendescribed in the U.S. Pat. No. 4,824,746.

The difficulties encountered in carrying out the rolling of thin lithiumfilms having a thickness that can range from 5 to 40 microns, forexample, are mainly due to the reactivity and to the adhesion of therolled metal to the materials with which they are in contact (e.g., therolling rollers, the plastic protection films, the rolling additives) aswell as to the poor mechanical properties of the thin strips. Forexample, a lithium film having a thickness of 20 μm and a width of 10 cmbreaks under a tensile stress of 579.13 kPa or more, which makes itimpossible to pull the film at the outlet of the rollers or to detachsaid film from the rolling rollers if the lithium film adheres ever soslightly to the rollers.

An approach normally used for the rolling or the calendering of hardmetals such as iron and nickel is based on the use of liquid rollingadditives such as organic solvents that can contain greases orlubricating agents. Examples include the fatty acids or derivativesthereof such as lauric acid or stearic acid, and the alcohols, forexample, EPAL 1012™ from Ethyl Corporation U.S.A., a mixture of linearC₁₀-C₁₂ primary alcohols. For lithium and, more particularly, forlithium intended for use in electrochemical cells, the use of suchadditives involves major drawbacks resulting from the reactivity of thelithium and/or the nonconductive nature of these additives.

According to an example, the chemical reactivity of the surface of thelithium in contact with solvents or lubricating agents includingreactive organic functions (organic acids or alcohols, for example) willcreate an electronically insulating passivation layer on the surface ofthe metal, thus limiting the proper operation of the electrochemicalcells, in particular in rechargeable batteries.

In a second example, the removal of the lubricating agent or greasesremaining in contact with the lithium after rolling is very difficult.These lubricating agents are electrical insulants and they are notsoluble in the electrolyte. When they are left on the films produced,they are thus detrimental to the proper operation of the lithiumelectrodes made therefrom. The washing of these agents on the surface ofthe lithium film generally leads to a contamination of the surface, thatis to say to lithium films of lesser quality.

The rolling methods that use lubricating agents for the more reliablepreparation of thin lithium films have been described in the U.S. Pat.Nos. 5,837,401 6,019,801. The lubricating agents used in these twopatents include polymers comprising solvating polymer chains. Thepreferred agents described therein are based on fatty acid diesters suchas polyoxyethylene distearates of formula:CH₃(CH₂)₁₆C(O)O(CH₂CH₂O)_(n)C(O)(CH₂)₁₆CH₃, in which n varies between 3and 100, the polymers having polyoxyethylene segments having a molecularweight equal to 200, 400 and 600 being preferable. The method describedin said patents enable the production, for example, of lithium filmshaving a length of 300 meters with a thickness of 25 μm±2 μm at a rateof about 20 m/min. It is generally described that these methods canreach a production rate of up to 50 m/min.

While this method was an improvement in comparison to the technologyavailable at the time, there still exists a need for the development ofnew improved lubricating agents, for example, achieving an increasedconductivity and/or enabling the obtention of electrochemical cells withan improved life span in cycles.

Modified polymers based on poly(octadecene-alt-maleic anhydride) filmson glass plates have been described in Schmidt et al., 2003, J. Appl.Polym. Sc., 87, 1255-1266. This document in fact refers to theincorporation of functionalized amines in the polymer and to the use ofglass plates obtained in studies of covalent immobilization of proteins,a use that is very different from that of lubricating agents in therolling of alkali metals.

BRIEF DESCRIPTION

According to a first aspect, the present application describes alubricating agent defined as a polymer of formula I:

in which

m is a positive whole number and denotes the number of repeated units Ain the polymer; n is zero or a positive whole number and denotes thenumber of repeated units B in the polymer, the repeated unit B beingabsent when n is zero, where m and n are selected so that the molecularweight of the polymer of Formula I is in the range from 1000 to 10⁶;

R¹, independently at each occurrence, is selected from the linear orbranched monovalent hydrocarbon radicals;

R², independently at each occurrence, is selected from —CH₂CH₂O— and—CH₂CH₂CH₂O—, where R² is bound to N by a carbon atom, or R² is absentand N is covalently bound to R⁴;

R³, independently at each occurrence, is selected from the linear orbranched monovalent hydrocarbon radicals;

R⁴, independently at each occurrence, is a polyether residue of formula—[CH(R⁵)CH₂O]_(s)CH₃, where 5≤s≤100; and

R⁵, independently at each occurrence, is H or CH₃.

According to an embodiment, m and n are selected so that the molecularweight of the lubricating agent of Formula I is in the range from 2000to 250,000, or from 2000 to 50,000, or even from 50,000 to 200,000.According to another embodiment, the ratio of the repeated units A:Bexpressed as mole percent in the polymer is in the range from 100:0 to10:90.

According to another embodiment, R¹, independently at each occurrence,is a linear or branched hydrocarbon radical of formula C_(r)H_(2r+1),where 4≤r≤24 or in which 8≤r≤18 and all the other groups are as definedabove. In another embodiment, R³, independently at each occurrence, is alinear or branched hydrocarbon radical of formula C_(t)H_(2t+1), where4≤t≤24, or in which 8≤t≤18, and all the other groups are as definedabove. In another embodiment, s is selected from the whole numbers from8 to 50, and all the other groups are as defined above.

According to another embodiment, R², at each occurrence, is a divalentradical of formula —CH₂CH₂O—, or R², at each occurrence, is a divalentradical of formula —CH₂CH₂CH₂O—, or even R² is absent, and all the othergroups are as defined above.

According to an embodiment, R⁴ is a polyether residue of formula—[CH(R⁵)CH₂O]_(s)CH₃, in which R⁵ is CH₃ at each occurrence, and all theother groups are as defined above. In another embodiment, R⁵ is ahydrogen atom at each occurrence, and all the other groups are asdefined above. According to another embodiment, R⁵, independently ateach occurrence, is CH₃ or hydrogen, such that R⁴ is a polyether residueincluding repeated units of propylene oxide (PO) and of ethylene oxide(EO), for example, in a molar ratio of PO:EO between about 20:1 andabout 1:30, or between about 10:1 and about 1:10. According to anexample, the polyether residue R⁴ has a molecular weight in the rangefrom about 300 g/mole to about 5000 g/mole, or from about 500 g/mole toabout 2500 g/mole.

According to another embodiment, the lubricating agent is selected fromthe Polymers 1 to 5 as defined in Table 1.

According to another aspect, the present application describes acomposition including a lubricating agent as defined here, jointly witha solvent that is inert with respect to the alkali metals. For example,the solvent is selected from the hydrocarbon solvents, the aromaticsolvents, and combinations thereof, that is to say systems of solventsincluding an aromatic solvent and a hydrocarbon solvent. The hydrocarbonsolvent can be selected from hexane and heptane, and the aromaticsolvent can be toluene. According to an embodiment, the compositionincludes the lubricating agent at a concentration from about 0.001% toabout 10% (weight/volume), or about 0.01% to about 5% (weight/v) of thetotal volume of the composition.

According to another aspect, the present application also describes analkali metal film having a first surface and a second surface, andincluding on at least one of the first and second surfaces, a thin layerof the lubricating agent or of the composition. For example, the alkalimetal film has a thickness in the range from about 5 μm to about 50 μm.According to an embodiment, the alkali metal is selected from lithium,the lithium alloys, sodium, and the sodium alloys, or lithium having apurity of at least 99% by weight, or a lithium alloy including less than3000 ppm of impurities by weight.

In another embodiment, the alkali metal film as defined here includes apassivation layer on at least one of the first and second surfacesthereof, possibly on the two surfaces thereof. For example, thepassivation layer can have a thickness of 500 Å or less, of 100 Å orless, or even of 50 Å or less. For example, the alkali metal is lithiumor a lithium alloy, and the passivation layer includes Li₂O, Li₂CO₃,LiOH, or a combination of at least two of said compounds.

According to yet another aspect, the present application describes amethod for producing an alkali metal film and the alkali metal film thusproduced, the method including the steps:

a) of application of a composition including a lubricating agent asdefined here on at least one of the first and second surfaces of analkali metal strip, in order to obtain a lubricated alkali metal strip;and

b) of rolling the lubricated alkali metal strip obtained in step (a)between at least two rollers, in order to produce an alkali metal film.

In an embodiment, at least steps (a) and (b) are performed in anessentially dry air atmosphere, for example, in an anhydrous chamber ora chamber with controlled humidity with a dew point between −45 and −55°C., for 0.7 to 2.2% relative humidity, preferably a dew point of about−50° C. and a relative humidity of about 1.3%.

According to another embodiment, the method includes, in addition, astep of obtention of the alkali metal strip, for example, by extrusionof an ingot or a rod made of an alkali metal.

According to another aspect, step (a) is carried out by the applicationof the composition on the strip at the inlet of the rollers and can alsobe carried out by a prior coating of the rolling rollers with or withoutadditional addition of composition directly onto the strip before step(b).

The alkali metal films as defined here can be used, among otherpurposes, for the production of electrodes and of electrochemical cellsthat include them in combination with an electrolyte and acounterelectrode, preferably both in the form of films. The electrolytecan be a nonaqueous liquid electrolyte including a compatible organicsolvent, a liquid electrolyte consisting of a molten salt, a polymerelectrolyte gel or a polymer electrolyte solid. The counterelectrodeincludes an active counterelectrode material as defined here or asgenerally used in the field.

DETAILED DESCRIPTION

The detailed description and the following examples are given forillustration and should not be interpreted as further limiting the scopeof the invention.

The term “about” as used in the present document means approximately, inthe region of, around. When the term “about” is used in connection witha numerical value, it modifies it by increasing or decreasing it by a10% variation with respect to the nominal value. This term can also takeinto account, for example, the experimental error of a measurementapparatus.

When a range of values is mentioned in the present application, thelower and upper limits of the range are always included in thedefinition, unless indicated otherwise.

I. The Lubricating Agents and the Compositions Thereof:

The polymers described here are useful as lubricating agents used inrolling alkali metal films. These agents are alkyl succinimide polyethercopolymers of Formula I:

in which

m and denote the number of repeated units A and B, respectively, in thepolymer, m being a positive whole number and n being a positive wholenumber or zero when the repeated unit B is absent, and where m and n areselected such that the molecular weight of the polymer of Formula I isin the range from 1000 to 10⁶, from 2000 to 250,000, from 2000 to100,000, from 2000 to 50,000, or even from 50,000 to 200,000, limitsincluded;

R¹, independently at each occurrence, is selected from the linear orbranched monovalent hydrocarbon radicals, preferably from the linear orbranched monovalent hydrocarbon radicals of formula C_(r)H_(2r+1), where4≤r≤24, preferably where 8≤r≤18;

R², independently at each occurrence, is selected from —CH₂CH₂O— and—CH₂CH₂CH₂O—, where R² is bound to N by a carbon atom, or R² is absentand N is covalently bound to R⁴;

R³, independently at each occurrence, is selected from the linear orbranched monovalent hydrocarbon radicals, preferably from the linear orbranched monovalent hydrocarbon radicals of formula C_(t)H_(2t+1), where4≤t≤24, preferably where 8≤t≤18;

R⁴, independently at each occurrence, is a polyether residue of formula—[CH(R⁵)CH₂O]_(s)CH₃, where 5≤s≤100, preferably where 8≤s≤50; and

R⁵, independently at each occurrence, is a hydrogen atom or a CH₃ group.

According to an embodiment, the ratio of the repeated units A:Bexpressed as mole percent in the lubricating agent is between 100:0 and10:90, preferably between 100:0 and 20:80, limits included. According toanother embodiment, the ratio of the repeated units A:B expressed asmole percent in the lubricating agent is between 60:40 and 10:90.

According to an embodiment, R⁴ is a polyether residue of formula—[CH(R⁵)CH₂O]_(s)CH₃, in which 5≤s≤100, and R⁵ is CH₃ at eachoccurrence, preferably where 8≤s≤50. In another embodiment, R⁴ is apolyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, in which 5≤s≤100, andR⁵ is a hydrogen atom at each occurrence, preferably where 8≤s≤50.According to a different mode, R⁴ is a polyether residue of formula apolyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, in which 5≤s≤100, andR⁵, independently at each occurrence, is CH₃ or hydrogen, preferablywhere 8≤s≤50, R⁴ thus being a polyether chain having repeated units ofpropylene oxide (PO) and of ethylene oxide (EO) (also referred to hereas a polyether chain PO/EO).

According to an embodiment, R⁴ is a polyether chain PO/EO covalentlybound to N (the nitrogen atom of a succinimide group). Examples of thesepolyether chains PO/EO include, without limitation, the polyethershaving a molar ratio PO/EO varying from about 20:1 to about 1:30, orfrom about 10:1 to about 1:10, preferably having a molecular weightbetween about 300 and about 5000, preferably about 500 and about 2500.Examples of R⁴ also include the polyether chains PO/EO of aminepolyethers, the amine group being part of the succinimide of the unit A,such as the monoamines Jeffamine® of the “M” series, for example, theM-600, M-1000, M-2005 and M-2070 (Huntsman Corporation, Texas, U.S.A.),having a respective molar content of PO:EO of 9:1, 3:19, 29:6 and 10:31.

According to an aspect, the content of repeated unit B in the polymer ofFormula I is adjusted in order to obtain a polymer that is soluble in asolvent or an apolar solvent system, for example, such a solvent orsystem of solvents includes hydrocarbon solvents (for example, hexane,heptane), aromatic solvents (for example, toluene), or mixtures thereof.

Nonlimiting examples of lubricating agent polymers of Formula I are asspecified in Table 1.

TABLE 1 Ratio A:B Molecular R⁴ (approx. weight Polymer R¹ R² R³ (PO:EO)mole %) (approx.) 1 C₁₆H₃₃ Absent Absent  3:19 100:0  5000 2 C₁₆H₃₃Absent Absent 10:31 100:0  5000 3 C₁₆H₃₃ Absent C₁₈H₃₇  3:19 33:67 145,000- 175,000 4 C₁₆H₃₃ Absent C₁₈H₃₇ 10:31 20:80  165,000- 195,000 5C₁₆H₃₃ Absent Absent 29:6  100:0  7000

For example, the lubricating agents of Formula I can be prepared by: (a)the obtention of an alternating (alt) copolymer of alkylene R₁CHCH₂ andof maleic anhydride, R₁ being as defined above. This copolymer is thenreacted with an amine of formula R₄-R₂—NH₂, optionally at the same time,beforehand or subsequently with an amine of formula R₃—NH₂, where R₂,R₃, and R₄ are as defined above. Examples of methods for producinglubricating agents are illustrated here in further detail in SynthesisExamples 1 to 4.

The compositions described here include at least one lubricating agentof Formula I. These compositions can also include additional componentssuch as solvents that are inert with respect to the alkali metals.Examples of solvents include, without limitation, the hydrocarbonsolvents (for example, hexane, heptane, etc.), the aromatic solvents(for example, toluene, etc.), or mixtures thereof.

II. Alkali Metal Films

The alkali metal films consist, for example, of lithium or of a lithiumalloy, of sodium or a sodium alloy, preferably of lithium or an alloy inwhich lithium is the major component, preferably lithium having a purityof at least 99% by weight, or a lithium alloy including less than 3000ppm of impurities by weight.

According to an embodiment, the alkali metal films as produced hereincludes on one of the two surfaces thereof or on said two surfaces, athin layer of lubricating agent of Formula I or of a compositionincluding it. For example, the lithium films including on one surface orone of the surfaces at least one lubricating agent or a composition ofthe invention can generally have a lower impedance in comparison tolithium films produced with the use of other lubricating additives.Other improved properties of these films can also comprise a more stableand more uniform passivation layer, and improved cycling properties.

When the method for producing the thin lithium film is performed in anessentially anhydrous air atmosphere, the passivation layer on thelithium film includes lithium carbonate, lithium oxide and/or lithiumhydroxide.

III. Method for the Production of Alkali Metal Films:

The alkali metal films as described here are produced by rolling orcalendering between rollers using the lubricating agents of Formula Iand the compositions including them. The methods for preparing lithiumfilms by metal rolling are illustrated, for example, in the U.S. Pat.Nos. 5,837,401 and 6,019,801 (both issued in the name of Gauthier etal.). The methods described in Gauthier et al. can be carried out usingthe lubricating agents and compositions as described here (for example,see Section I above).

For example, a lithium strip having a thickness of about 250 μm is usedin the rolling process in order to produce a lithium film. The lithiumstrips can be obtained, for example, by extrusion of commerciallyavailable ingots or rods made of lithium.

In general, a lithium strip, mounted beforehand on an unwinder, ispassed between two work rollers. A lubricant is added (for example, bymeans of a pouring spout onto the strip and/or by prior coating of thework rollers) at the point of insertion of the lithium strip between thetwo rollers, that is to say immediately before the rolling step.According to an embodiment, the lithium film that comes out of the workrollers can be wound on a winder for later use. In this particular mode,the lubricant acts, at least in part, so as to prevent the adhesion ofthe lithium film to itself. According to another embodiment, thelubricated lithium film produced is used directly for other rollingsteps (for example, by continuous or series rolling) with a layer ofsolid polymer electrolyte, a protective layer, and/or a currentcollector (for example, in a current collector/lithium film/electrolyteconfiguration or in a current collector/lithium film/protectivelayer/electrolyte) configuration. In each case, the winders or rollersarranged in series supply a sufficient tension to the lithium film inorder to reduce the adhesion of the lithium film to the work rollers,but without excessive tension so as to prevent the tearing of thelithium film.

For example, the step of rolling between rollers can produce an alkalimetal film at a rate in the range from about 10 m/min to about 50 m/minof alkali metal film.

It is obvious that the work rollers have to consist of and/or be coatedwith a material that is inert with respect to the alkali metal (such asmetal lithium) in the presence of the lubricating agent and/or thecomposition of the invention. For example, the rollers can consist ofhard polymers such as plastics, metal rollers coated with plasticmaterial, rollers made of stainless steel, etc.

The method of the invention can be carried out in an anhydrousatmosphere, preferably in an essentially dry air atmosphere, forexample, in an anhydrous chamber or a chamber with controlled humidity,for example, with a dew point between −45 and −55° C., for a relativehumidity from 0.7 to 2.2%, preferably a dew point of about −50° C. for1.3% of relative humidity.

IV. Electrochemical Cells:

The alkali metal films as produced here are useful for producingelectrochemical cells. For example, the electrochemical cells include atleast one electrode having an alkali material film, such as lithium, asactive electrode material, a counterelectrode, and an electrolytebetween the electrode and the counterelectrode. An option concerns theelectrochemical cells including a plurality of arrangements (forexample, a plurality of electrode/electrolyte/counterelectrode orcounterelectrode/electrolyte/electrode/electrolyte/counterelectrodearrangements). For example, the cell can be a multilayer material whichcan be folded or rolled the form of a cylinder.

Electrochemical cells in which the lithium films described here couldalso be used also comprise the lithium-air electrochemical cells such asthose described in the PCT application published under numberWO2012/071668 (Zaghib et al.).

According to an aspect, the polymer of Formula I or the compositionthereof can be present on the surface between the lithium film and theadjacent layer thereof (for example, the current collector, theelectrolyte, etc.), or it can be in part or completely diffuse,dispersed or dissolved in the electrolyte. According to another aspect,the lubricating agent (or the composition thereof) is present betweenthe electrode and the electrolyte and is ion conductive, for example,due to its dissolving the lithium salts present in the electrolyte.

According to a preferred embodiment, the electrochemical cell includinga lithium film as described here, is sealed or included in the interiorof a sealed compartment.

a. Electrode:

An electrode includes at least one alkali metal film as described inSection II or as prepared by the process of Section III. Preferably, thealkali metal film of the electrode is an active lithium film or an alloyin which lithium is the majority component, preferably lithium having apurity of at least 99% by weight, or a lithium alloy including less than3000 ppm of impurities by weight.

According to an embodiment, the electrode includes, in addition, acurrent collector made of a metal layer such as, for example, a nickelor copper layer adhering to the surface of the alkali metal filmopposite the surface that faces or will face the electrolyte layer.

Optionally, an ion conductive protective layer can be present betweenthe alkali metal film (for example, Li, Na, or an alloy of either) andthe electrolyte, for example, in order to protect the lithium filmagainst degradation and/or in order to prevent the formation ofdendrites. An ion conductive protective layer, for example, an ionconductive polymer, a ceramic (for example, a lithium and phosphorusoxynitride (LIPON), etc.), glass, or a combination of two or more ofsaid materials can be applied to the surface of the lithium film or ofthe electrolyte layer (for example, of a solid polymer electrolyte)before the assembly. The vitreous or ceramic protective layers areapplied using standard processes such as cathodic atomization, ablationby laser or plasma. Examples of protective layers are described in thePCT application published under number WO2008/009107 (Zaghib et al.).

b. Electrolyte:

The electrolytes used in these electrochemical cells include anyelectrolyte compatible with the use of electrodes made of active lithiumfilm or of another alkali metal. Examples of such electrolytes include,without limitations, nonaqueous liquid electrolytes, gel polymerelectrolytes, and solid polymer electrolytes. The following electrolytesare given as illustrative examples and should not be interpreted to belimiting.

For example, the compatible liquid electrolytes comprise the organicliquid electrolytes including an aprotic polar solvent such as ethylenecarbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC),dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), γ-butyrolactone(γ-BL), vinyl carbonate (VC), and mixtures thereof, and lithium saltssuch as LiTFSI, LiPF₆, etc. Other examples of compatible liquidelectrolytes comprise the molten salt electrolytes including lithiumsalts such as lithium chloride, lithium bromide, lithium fluoride, andcompositions including them, or organic salts. Nonlimiting examples ofliquid electrolytes of molten salts can be found in US2002/0110739(McEwen et al.). The liquid electrolyte can impregnate a separator suchas a polymer separator (for example, made of polypropylene, polyethyleneor of a copolymer thereof.

The compatible gel polymer electrolytes can include, for example,polymer precursors and lithium salts (such as LiTFSI, LiPF₆, etc.), anaprotic polar solvent as defined above, a polymerization/crosslinkinginitiator when they are needed. Examples of such gel electrolytescomprise, without limitations, the gel electrolytes described in the PCTapplications published under numbers WO2009/111860 (Zaghib et al.) andWO2004/068610 (Zaghib et al.). A gel electrolyte can also impregnate aseparator as defined above.

The solid polymer electrolytes (SPE) can generally include one or morepolar solid polymers which can be crosslinked or not, and salts, forexample, lithium salts such as LiTFSI, LiPF₆, LiDCTA, LiBETI, LiFSI,LiBF₄, LiBOB, etc. Polyether type polymers such as polymers based onpolyethylene oxide (PEO) can be used, but several other polymerscompatible with lithium are also known for producing SPE. Examples ofsuch polymers include the multi-branch polymers in the shape of a staror comb, such as those described in the PCT application published underNo. WO2003/063287 (Zaghib et al.).

c. Counterelectrode

The counterelectrodes include at least one electrochemically activematerial (EAM) compatible with the use of alkali metal electrodes and,in particular, metal lithium. Any counterelectrode EAM known from thefield can be used in these electrochemical cells. For example, thecounterelectrode EAM can operate at a voltage within the range of about1 V to about 5 V. Examples of counterelectrode EAM can be found, forexample, in Whittingham M. S. (2004), Chem. Rev., 104, 4271-4301, whichis incorporated here by reference in its entirety and for all purposes.

For an electrode including a lithium film, nonlimiting examples ofcounterelectrode EAM include the lithium titanates (for example:Li₄Ti₅O₁₂), sulfur or materials including sulfur, the lithium and metalphosphates (for example, LiM′PO₄ where M′ is Fe, Ni, Mn, Co, orcombinations thereof), the vanadium oxides (for example: LiV₃O₈, V₂O₅,etc.), and the lithium and metal oxides, such as LiMn₂O₄, LiM″O₂ (M″being Mn, Co, Ni or combinations thereof), Li(NM′″)O₂ (M′″ being Mn, Co,Al, Fe, Cr, Ti, Zr, etc., or combinations thereof.

Similarly, the EAM of the counterelectrode, when the electrode includesa sodium film, are known to the person skilled in the art. For example,they include sulfur or a material including sulfur, sodium phosphates,and one or more metals (for example: Na₂FePO₄F, Na₂FeP₂O₇F, NaVPO₄F,NaV_(1-x)Cr_(x)PO₄F, where x<1, for example, 0<x<0.1), or sodium andmetal sulfates (for example: Na₂Fe₂(SO₄)₃). The counterelectrode EAM canalso be oxygen in a lithium-air or sodium-air cell depending on thealkali metal of the electrode.

The counterelectrode can also include an electronic conducting materialsuch as a carbon source, including, for example, Ketjen® carbon,Shawinigan carbon, graphite, vapor grown carbon fibers (VGCF),non-powder carbon obtained by the carbonization of an organic precursor,and a combination of two or more of said materials. The carbon used canbe of natural or synthetic origin.

The counterelectrode can be a composite counterelectrode that includes,in addition, a polymer binder, and, optionally, an alkali metal saltsuch as the lithium salts (for example: LiTFSI, LiDCTA, LiBETI, LiFSI,LiPF₆, LiBF₄, LiBOB, etc.) or the sodium salts (for example: NaClO₄,NaPF₆, etc.).

The following examples illustrate the invention and should not beinterpreted as limiting the scope of the invention as described.

EXAMPLES

In order to evaluate the effect of the lubricant on the surface of alithium film, and the resulting properties, lithium films having athickness of 27 μm, produced according to the procedure described in theU.S. Pat. No. 6,019,801 were immersed in the lubricants tested. Thelubricated films were then inserted in electrochemical cells and theirproperties were measured.

The components used in the Examples below are defined as follows:

PEO(200) distearate: PEO-200 distearate as described in the U.S. Pat.No. 6,019,801.

SPE: “Solid Polymer Electrode” based on a polyether polymer as describedin the U.S. Pat. Nos. 6,903,174 and 6,855,788 including LiTFSI aslithium salt in a ratio of 30/1 (oxygen v. Li).

Polymer 1: is a polymer of Formula I having a molecular weight of about5000, in which the unit B is absent, R¹ is C₁₆H₃₃, R² is absent, and R⁴is covalently bound to N and represents the Jeffamine® M-1000 residue, apolyetheramine having a ratio PO/EO of 3/19.

Polymer 2: is a polymer of Formula I having a molecular weight of about5000, in which the unit B is absent, R¹ is C₁₆H₃₃, R² is absent, and R⁴is covalently bound to N and represents the Jeffamine® M-2070 residue, apolyetheramine having a ratio PO/EO of 10/31.

C—LiFePO₄: LiFePO₄ coated with carbon

Example 1 (Comparative)

A lubricant was prepared by the addition of 1% by weight of PEO(200)distearate to a mixture of toluene and hexane (80:20 (vol:vol), bothanhydrous). A lithium film having a thickness of 27 μm is then immersedin this lubricant for 5 minutes.

a. Symmetric Cell A 4 cm² cell was assembled in the laboratory accordingto the configuration Li/SPE/Li The initial impedance of the Li/SPE/Licell at 80° C. was 15 ohms. After six weeks, the impedance reached 111ohms, showing a 640% increase of the impedance.

b. Asymmetric Cell

A 4 cm² cell was assembled in the laboratory according to theconfiguration C—LiFePO₄/SPE/Li. The cell was then discharged at a C/4rate and charged at a C/4 rate to a voltage of 2.5 V to 3.8 V at 80° C.The initial capacity of the cell was 158 mAh/g. After 350 cycles, thecapacity reached 80% of the initial capacity.

Example 2

The lubricant was prepared by the addition of 1% by weight of Polymer 1to a mixture of toluene and hexane (80:20 (vol:vol), both anhydrous). Alithium film having a thickness of 27 μm was then immersed into thislubricant for about 5 minutes.

a. Symmetric Cell

A 4 cm² cell was assembled in the laboratory according to theconfiguration Li/SPE/Li. The initial impedance of the cell ofconfiguration Li/SPE/Li at 80° C. was 22 ohms. After six weeks, theimpedance reached 48 ohms, showing a 120% increase of the impedance.

b. Asymmetric Cell

A 4 cm² cell was assembled in the laboratory according to theconfiguration C—LiFePO₄/SPE/Li as in Example 1(b). The cell was thendischarged at a C/4 rate and charged at a C/4 rate to a voltage of 2.5 Vto 3.8 V at 80° C. The initial capacity of the cell was 160 mAh/g. After1100 cycles, the capacity reached 80% of the initial capacity.

c. Conclusions

The increase of the impedance is lower in this cell than in that ofExample 1, where a lubricant based on PEO(200) distearate was used. Theuse of a lubricant based on Polymer 1 results in a stable and moreuniform passivation layer on the surface of the lithium. The cellincorporating the lithium film including a thin layer of Polymer 1resulted in an improved life span in cycles compared to the celldescribed in Example 1.

Example 3

The lubricant was prepared by the addition of 1% by weight of Polymer 2to a mixture of toluene and hexane (80:20 (vol:vol), both anhydrous). Alithium film having a thickness of 27 μm was then immersed in thislubricant for about 5 minutes.

a. Symmetric Cell

A 4 cm² cell was assembled in the laboratory according to theconfiguration Li/SPE/Li. The initial impedance of the cell having theconfiguration Li/SPE/Li at 80° C. was 23 ohms. After six weeks, theimpedance reached 45 ohms, showing a 96% increase of the impedance.

b. Asymmetric Cell

A 4 cm² cell was assembled in the laboratory according to theconfiguration C—LiFePO₄/SPE/Li as in Example 1(b). The cell was thendischarged at a C/4 rate and charged at a C/4 rate to a voltage of 2.5 Vto 3.8 V at 80° C. The initial capacity of the cell was 161 mAh/g. After1300 cycles, the capacity reached 80% of the initial capacity (a 20%lowering).

c. Conclusions

The increase of the impedance is lower for this cell than for that ofExample 1(b), where the lubricant based on PEO(200) distearate was used.The use of the lubricant based on Polymer 2 also results in a verystable and more uniform passivation layer on the lithium surface. Thiscell also resulted in an improved life span in cycles compared to thecell described in Example 1(b).

Synthesis Example 1

36.26 g of a commercial poly(octadecene-alt-maleic anhydride) polymer(M_(w)=65.000) are dissolved in 250 mL of toluene under stirring at roomtemperature. Octadecylamine (18 g) in 100 mL of toluene is addeddropwise to the solution under stirring over a time period of 2 hours.Then, 40 g of Jeffamine® of type M-1000 (XTJ-506) with a ratio PO/EO of3:19 diluted in 50 mL of toluene are added rapidly and still understirring. The resulting ternary solution is then placed in a 500 mLround-bottom flask equipped with a Dean-Stark apparatus and a condenser.The solution is heated at reflux for 8 hours, a time period during whichthe water released during the formation of the imide gradually appearsin the burette of the Dean-Stark apparatus.

The resulting viscous polymer solution is then filtered and evaporatedin a rotary evaporator. The sticky substance obtained is redissolved in625 mL of heptane and washed 5 times with a volume of 100 mL of anaqueous solution of sulfuric acid (H₂SO₄) at 0.1 M in order to eliminatethe excess of Jeffamine®. The extraction of the Jeffamine® is thenfollowed by a rinsing with 5 portions of demineralized water. The dryingof the heptane solution is carried out by the addition of 40 g of 4 Åmolecular sieve which was treated beforehand under a vacuum at 200° C.The solution at 10% (weight/volume) of Polymer 3 in heptane thusobtained is ready for dilution and/or subsequent use in the rolling ofan alkali metal such as lithium.

Synthesis Example 2

36.26 g of a commercial poly(octadecene-alt-maleic anhydride) polymer(M_(w)=65.000) and 11 g of trimethylamine are dissolved in 250 mL oftoluene under stirring at room temperature. Octadecylamine (21.5 g) in100 mL of toluene is added dropwise to the solution under stirring overa time period of 2 hours. Then, 45 g of Jeffamine® of type M-2070 with aratio PO/EO of 10:31 dissolved in 100 mL of toluene are added rapidlyand still under stirring. The resulting quaternary solution is thenplaced in a 500 mL round-bottom flask equipped with a Dean-Starkapparatus and a condenser. The solution is heated at reflux for 8 hours,a time period during which water released during the formation of theimide gradually appears in the burette of the Dean-Stark apparatus.

The resulting viscous polymer solution is then filtered and evaporated.The waxy substance obtained is redissolved in 900 mL of heptane andwashed 5 times with a volume of 200 mL of an aqueous sulfuric acidsolution (H₂SO₄) at 0.1 M in order to eliminate the Jeffamine® andtrimethylamine excess. The extraction is then followed by a rinsing with5 portions of demineralized water. The drying of the heptane solution iscarried out by adding 40 g of 4 Å molecular sieve treated beforehandunder a vacuum at 200° C. The solution at 10% (weight/volume) of Polymer4 in heptane thus obtained is ready for dilution and/or subsequent usein the rolling of an alkali metal such as lithium.

Synthesis Example 3

10 g of commercial maleic anhydride (Aldrich) are added to a solution of105 g of Jeffamine® M-1000 (Huntsman corporation) in 300 mL of toluene.The reaction mixture is submitted to a Dean-Stark dehydration in orderto carry out the imidization of the terminal NH₂ groups of the Jeffaminefor 5 hours. The clear solution obtained is cooled to a temperature of0° C., and 25.8 g of 1-octadecene and 1.3 g of azobis(isobutyronitrile)are added. The mixture is deaerated by nitrogen bubbling (100 mL/min)for one hour. The neutral gas sweeping is stopped, and the reactionmixture is heated to 80° C. for 24 hours. The solution which has aslightly brown coloration is washed three times with a 0.1 M sulfuricacid solution, then it is washed again three times with pure water. Thesupernatant solution is separated, and the toluene is evaporated. Theresult is a viscous liquid having a molecular weight of about 5000 g/mol(Polymer 1) which can be used in a rolling process.

Synthesis Example 4

In a manner similar to Synthesis Example 3, 10 g of commercial maleicanhydride (Aldrich) are added to a solution of 210 g of Jeffamine®M-2070 (Huntsman corporation) in 500 mL of toluene. The reaction mixtureis subjected to a Dean-Stark dehydration for 5 hours. The clear solutionobtained is cooled to a temperature of 0° C., and 25.8 g of 1-octadeceneand 1.6 g of azobis(isobutyronitrile) are added. The mixture isdeaerated by nitrogen bubbling (100 mL/min) for one hour. The neutralgas sweeping is stopped, and the reaction mixture is heated to 80° C.for 24 hours. The solution which has a slightly brown coloration iswashed three times with a 0.1 M sulfuric acid solution, then again threetimes with pure water. The supernatant solution is separated, and thetoluene is evaporated. The result is a viscous liquid having a molecularweight of about 5000 g/mol (Polymer 2) which can be used in a rollingprocess.

Numerous modifications could be made to any of the embodiments describedabove without going beyond the scope of the invention as conceived. Thereferences, patents or documents of the scientific literature mentionedin the present application are incorporated here by reference in theirentirety and for all purposes.

Embodiments

1. A lubricating agent consisting of a polymer of Formula I

in which

m and n denote the number of repeated units A and B, respectively, inthe polymer; m being a positive whole number and n being a positivewhole number or zero when the repeated unit B is absent, and where m andn are selected so that the molecular weight of the polymer of Formula Iis in the range from 1000 to 10⁶;

R¹, independently at each occurrence, is selected from the linear orbranched monovalent hydrocarbon radicals;

R², independently at each occurrence, is selected from —CH₂CH₂O— and—CH₂CH₂CH₂O—, where R² is bound to N by a carbon atom, or R² is absentand N is covalently bound to R⁴;

R³, independently at each occurrence, is selected from the linear orbranched monovalent hydrocarbon radicals;

R⁴, independently at each occurrence, is a polyether residue of formula—[CH(R⁵)CH₂O]_(s)CH₃, where 5≤s≤100; and

R⁵, independently at each occurrence, is a hydrogen atom or a CH₃ group.

2. The lubricating agent according to embodiment 1, in which m and n areselected so that the molecular weight of the lubricating agent ofFormula I is in the range from 2000 to 250,000.

3. The lubricating agent according to embodiment 1 or 2, in which m andn are selected so that the molecular weight of the lubricating agent ofFormula I is in the range from 2000 to 50,000.

4. The lubricating agent according to embodiment 1 or 2, in which m andn are selected so that the molecular weight of the lubricating agent ofFormula I is in the range from 50,000 to 200,000.

5. The lubricating agent according to any one of embodiments 1 to 4, inwhich R¹, independently at each occurrence, is a linear or branchedhydrocarbon radical of formula C_(r)H_(2r+1), where 4≤r≤24.

6. The lubricating agent according to any one of embodiments 1 to 5, inwhich R¹, independently at each occurrence, is a linear or branchedhydrocarbon radical of formula C_(r)H_(2r+1), where 8≤r≤18.

7. The lubricating agent according to any one of embodiments 1 to 6, inwhich R³, independently at each occurrence, is a linear or branchedhydrocarbon radical of formula C_(t)H_(2t+1), where 4≤t≤24.

8. The lubricating agent according to any one of embodiments 1 to 7, inwhich R³, independently at each occurrence, is a linear or branchedhydrocarbon radical of formula C_(t)H_(2t+1), where 8≤t≤18.

9. The lubricating agent according to any one of embodiments 1 to 8, inwhich 8≤s≤50.

10. The lubricating agent according to any one of embodiments 1 to 9, inwhich the ratio of the repeated units A:B expressed as mole percent inthe polymer is in the range from 100:0 to 10:90.

11. The lubricating agent according to any one of embodiments 1 to 10,in which R² is a divalent radical of formula —CH₂CH₂O—.

12. The lubricating agent according to any one of embodiments 1 to 10,in which R² is a divalent radical of formula-CH₂CH₂CH₂O—.

13. The lubricating agent according to any one of embodiments 1 to 10,in which R² is absent.

14. The lubricating agent according to any one of embodiments 1 to 13,in which R⁴ is a polyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, inwhich R⁵ is CH₃ at each occurrence.

15. The lubricating agent according to any one of embodiments 1 to 13,in which R⁴ is a polyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, inwhich R⁵ is a hydrogen at each occurrence.

16. The lubricating agent according to any one of embodiments 1 to 13,in which R⁴ is a polyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, andin which R⁵, independently at each occurrence, is CH₃ or hydrogen, suchthat R⁴ is a polyether residue including repeated units of propyleneoxide (PO) and of ethylene oxide (EO).

17. The lubricating agent according to embodiment 16, in which thepolyether residue has a molar ratio of PO:EO between about 20:1 andabout 1:30.

18. The lubricating agent according to embodiment 17, in which the molarratio of PO:EO is between about 10:1 and about 1:10.

19. The lubricating agent according to any one of embodiments 14 to 18,in which the polyether residue has a molecular weight between about 300g/mole and about 5000 g/mole.

20. The lubricating agent according to any one of embodiments 14 to 19,in which the polyether residue has a molecular weight between about 500and about 2500 g/mole.

21. The lubricating agent according to embodiment 1, in which thelubricating agent is selected from Polymers 1 to 5 as defined in Table1.

22. A composition including a lubricating agent according to any one ofembodiments 1 to 21 jointly with a solvent that is inert with respect tothe alkali metals.

23. The composition according to embodiment 22, in which the solvent isselected from the hydrocarbon solvents, the aromatic solvents andmixtures thereof.

24. The composition according to embodiment 23, in which the solvent isa system of solvents, including at least one aromatic solvent and atleast one hydrocarbon solvent.

25. The composition according to embodiment 23 or 24, in which thehydrocarbon solvent is selected from hexane and heptane.

26. The composition according to embodiment 23 or 24, in which thearomatic solvent is toluene.

27. The composition according to any one of embodiments 22 to 26, inwhich the lubricating agent is present at a concentration from about0.001% to about 10% (weight/volume) with respect to the total volume ofthe composition.

28. The composition according to embodiment 27, in which the lubricatingagent is present at a concentration in the range from about 0.01% toabout 5% (weight/volume) with respect to the total volume of thecomposition.

29. An alkali metal film having a first surface and a second surface,and including on at least one of the first and second surfaces, a thinlayer of the lubricating agent as defined in any one of embodiments 1 to21 or of the composition as defined in any one of embodiments 22 to 28.

30. The alkali metal film according to embodiment 29, having a thicknessin the range from about 5 μm to about 50 μm.

31. The alkali metal film according to embodiment 29 or 30, in whichsaid alkali metal is selected from lithium, the lithium alloys, sodium,and the sodium alloys.

32. The alkali metal film according to embodiment 31, in which thealkali metal is lithium having a purity of at least 99% by weight, or alithium alloy including at least 3000 ppm of impurities by weight.

33. The alkali metal film according to any one of embodiments 29 to 32,including a passivation layer on at least one of the first and secondsurfaces thereof.

34. The alkali metal film according to embodiment 33, including apassivation layer on the first and second surfaces thereof.

35. The alkali metal film according to any one of embodiment 33 or 34,in which the passivation layer has a thickness of 100 Å or less or of 50Å or less.

36. The alkali metal film according to any one of embodiments 33 to 35,in which the alkali metal is lithium or a lithium alloy, and thepassivation layer includes Li₂O, Li₂CO₃, LiOH or a combination of atleast two of said compounds.

37. A method for producing an alkali metal film, the method includingthe steps of:

a) application of a composition according to any one of embodiments 22to 28 on at least one of the first and second surfaces of an alkalimetal strip, in order to obtain a lubricated alkali metal strip; and

b) rolling the lubricated alkali metal strip obtained in step (a)between at least two rollers, in order to produce an alkali metal film.

38. The method according to embodiment 37, which is performed in anessentially dry air atmosphere.

39. The method according to embodiment 37 or 38, which is performed inan anhydrous chamber or a chamber with controlled humidity with a dewpoint between −45 and −55° C., for 0.7 to 2.2% relative humidity.

40. The method according to embodiment 39, in which the anhydrouschamber or the chamber with controlled humidity with a dew point ofabout −50° C. for a relative humidity of about 1.3%.

41. The method according to any one of embodiments 37 to 40, whichincludes, in addition, a step of obtention of the alkali metal strip,used in step (a), by extrusion of an ingot or rod made of an alkalimetal.

42. The method according to any one of embodiments 37 to 41, in whichstep (a) is carried out by the application of the composition on thestrip at the inlet of the rollers and/or by prior coating of the rollingrollers with or without additional addition of composition directly ontothe strip before step (b).

43. The alkali metal film produced by a method as defined in any one ofembodiments 37 to 42.

44. The alkali metal film according to embodiment 43, having a thicknessin the range from about 5 μm to about 50 μm.

45. The alkali metal film according to embodiment 43 or 44, in whichsaid alkali metal is selected from lithium, the lithium alloys, sodium,and the sodium alloys.

46. The alkali metal film according to embodiment 45, in which thealkali metal is lithium having a purity of at least 99% by weight, or alithium alloy including less than 3000 ppm of impurities by weight.

47. The alkali metal film according to any one of embodiments 43 to 46,including a stable and uniform passivation layer on at least one of thefirst and second surfaces thereof.

48. The alkali metal film according to embodiment 47, including apassivation layer on the first and second surfaces thereof.

49. The alkali metal film according to embodiments 47 or 48, in whichthe passivation layer has a thickness of 100 Å or less, or of 50 Å orless.

50. The alkali metal film according to any one of embodiments 47 to 49,in which said alkali metal is lithium or a lithium alloy, and thepassivation layer includes Li₂O, Li₂CO₃, LiOH or a combination of atleast two of said compounds.

51. An electrode including an alkali metal film as defined in any one ofembodiments 29 to 36 and 43 to 50.

1. (canceled)
 2. An alkali metal film having a first surface and asecond surface, and comprising on at least one of the first and secondsurfaces, a thin layer of a lubricating agent, the lubricating agentconsisting of a polymer of Formula I:

wherein, m and n denote the number of repeated units A and B,respectively, in the polymer; m being a positive whole number and nbeing a positive whole number or zero when the repeated unit B isabsent, and where m and n are selected so that the molecular weight ofthe polymer of Formula I is in the range from 1000 to 10⁶; R¹ isindependently at each occurrence selected from linear or branchedmonovalent hydrocarbon radicals; R² is independently at each occurrenceselected from —CH₂CH₂O— and —CH₂CH₂CH₂O—, where R² is bound to N by acarbon atom, or R² is absent and N is covalently bound to R⁴; R³ isindependently at each occurrence selected from the linear or branchedmonovalent hydrocarbon radicals; R⁴ is independently at each occurrencea polyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, wherein 5≤s≤100;and R⁵ is independently at each occurrence a hydrogen atom or a CH₃group.
 3. The alkali metal film of claim 2, wherein m and n are selectedso that the molecular weight of the lubricating agent of Formula I is inthe range from 2000 to 250,000.
 4. The alkali metal film of claim 3,wherein m and n are selected so that the molecular weight of thelubricating agent of Formula I is in the range from 2000 to 50,000. 5.The alkali metal film of claim 3, wherein m and n are selected so thatthe molecular weight of the lubricating agent of Formula I is in therange from 50,000 to 200,000.
 6. The alkali metal film of claim 2,wherein R¹ is independently at each occurrence a linear or branchedhydrocarbon radical of formula C_(r)H_(2r+1), wherein 4≤r≤24.
 7. Thealkali metal film of claim 2, wherein R¹ is independently at eachoccurrence a linear or branched hydrocarbon radical of formulaC_(r)H_(2r+1), wherein 8≤r≤18.
 8. The alkali metal film of claim 2,wherein R³ is independently at each occurrence a linear or branchedhydrocarbon radical of formula C_(t)H_(2t+1), wherein 4≤t≤24.
 9. Thealkali metal film of claim 2, wherein R³ is independently at eachoccurrence a linear or branched hydrocarbon radical of formulaC_(t)H_(2t+1), wherein 8≤t≤18.
 10. The alkali metal film of claim 2,wherein 8≤s≤50.
 11. The alkali metal film of claim 2, wherein the ratioof the repeated units A:B expressed as mole percent in the polymer is inthe range from 100:0 to 10:90.
 12. The alkali metal film of claim 2,wherein R² is a divalent radical of formula —CH₂CH₂O—.
 13. The alkalimetal film of claim 2, wherein R² is a divalent radical of formula—CH₂CH₂CH₂O—.
 14. The alkali metal film of claim 2, wherein R² isabsent.
 15. The alkali metal film of claim 2, wherein R⁴ is selectedfrom: (a) a polyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, whereinR⁵ is CH₃ at each occurrence; (b) a polyether residue of formula—[CH(R⁵)CH₂O]_(s)CH₃, wherein R⁵ is a hydrogen at each occurrence; and(c) a polyether residue of formula —[CH(R⁵)CH₂O]_(s)CH₃, and in which R⁵is independently at each occurrence CH₃ or hydrogen, such that R⁴ is apolyether residue including repeated units of propylene oxide (PO) andof ethylene oxide (EO).
 16. The alkali metal film of claim 15, whereinthe polyether residue has a molar ratio of PO:EO between about 20:1 andabout 1:30.
 17. The alkali metal film of claim 16, wherein the molarratio of PO:EO is between about 10:1 and about 1:10.
 18. The alkalimetal film of claim 15, wherein the polyether residue has a molecularweight between about 300 g/mole and about 5000 g/mole.
 19. The alkalimetal film of claim 15, wherein the polyether residue has a molecularweight between about 500 g/mole and about 2500 g/mole.
 20. The alkalimetal film of claim 3, having a thickness in the range from about 5 μmto about 50 μm.
 21. The alkali metal film of claim 3, wherein saidalkali metal is selected from lithium, lithium alloys, sodium, andsodium alloys.
 22. The alkali metal film of claim 21, wherein the alkalimetal is lithium having a purity of at least 99% by weight, or a lithiumalloy including at least 3000 ppm of impurities by weight.
 23. Thealkali metal film of claim 3, further comprising a passivation layer onat least one of the first and second surfaces thereof.
 24. The alkalimetal film of claim 3, further comprising a passivation layer on thefirst and second surfaces thereof.
 25. The alkali metal film of claim23, wherein the passivation layer has a thickness of 100 Å or less or of50 Å or less.
 26. The alkali metal film of claim 23, wherein the alkalimetal is lithium or a lithium alloy, and the passivation layer includesLi₂O, Li₂CO₃, LiOH or a combination of at least two thereof.
 27. Thealkali metal film of claim 2, further comprising a solvent that is inertwith respect to alkali metals.
 28. The alkali metal film of claim 3,further comprising a solvent that is inert with respect to alkalimetals.